$ cat t.pl
#!/usr/bin/perl
use strict; use warnings;
my @array = <DATA>;
foreach my $line (@array) {
   if ($line =~ /mail: /) {
      my $mail = substr($line, $+[$#+] );
      print "mail=$mail\n";
   }
}
__DATA__
This @ should be just fine
mail: this @ should also be fine

$ perl t.pl
mail=this @ should also be fine